For now, KMS caused only problems for me.
KMS does (AFAIK):
Flicker-free boot experience and "graphical" text mode - i dont see their relevance until the OSS drivers are fixed to have the same level of reliance as nvidia's.
The reduced boot time is not brought by KMS/Plymouth, but mainly by rearranging the start order of services... Also, i dont care about + 10-20-30 sec boot difference if afterwards i have a system that is rock steady and its reliable.
These graphical bells and whistles really should wait until the OSS drivers mature enough to be stable - i would say the devs should channel their energy to make better/more stable drivers not introducing new features that are purely (maybe i am mistaken here, but this is all i see) cosmetic in nature.
I am a Nvidia user but i(and not only i suppose) would really like an Intel driver that is stable and uses the 4500's full capacity - there are tons of cheap laptops out there with this card and i have to look for nvidias because those have the only stable Linux drivers.

For now, KMS caused only problems for me.
KMS does (AFAIK):
Flicker-free boot experience and "graphical" text mode - i dont see their relevance until the OSS drivers are fixed to have the same level of reliance as nvidia's.
The reduced boot time is not brought by KMS/Plymouth, but mainly by rearranging the start order of services... Also, i dont care about + 10-20-30 sec boot difference if afterwards i have a system that is rock steady and its reliable.
These graphical bells and whistles really should wait until the OSS drivers mature enough to be stable - i would say the devs should channel their energy to make better/more stable drivers not introducing new features that are purely (maybe i am mistaken here, but this is all i see) cosmetic in nature.
I am a Nvidia user but i(and not only i suppose) would really like an Intel driver that is stable and uses the 4500's full capacity - there are tons of cheap laptops out there with this card and i have to look for nvidias because those have the only stable Linux drivers.

They are trying to make the OSS driver stable but KMS and such features are wanted because it's 2010. KMS reduces the time between the end of the boot process and Xorg starting, making it seamless. The Nouveau driver will take years to be fully up to par, no thanks to NVIDIA. These "bells and whistles" you talk about should be standard in any modern driver and it's the easiest part because they're open-source and part of the kernel anyway.

Fedora 13 and the NVIDIA binary work just fine with Plymouth for me, unlike Ubuntu.

gradinaruvasile
KMS is not only flicker-free boot and boot speedup. Around a year ago, some people tried to run X-server not as root, but as regular user and it's requires KMS, so KMS can provide enchanted security.